At present, recording materials which comprise chromogenic dyes which are colorless or substantially colorless in themselves but form colors by the action of acidic substances brought into intimate contact therewith (said dyes are hereinafter called "chromogenic dyes") and said acidic substances (color developers) which permit said chromogenic dyes to form colors have been extensively used for, e.g., pressure-sensitive copying papers, heat-sensitive recording papers and the like. Keeping pace with the speeding-up of the services of communication recording devices such as facsimile, it is desired that the color developing speed of the heat-sensitive recording papers used in facsimile is accelerated. For heat-sensitive recording papers for use in facsimile, there have been mostly used black color forming chromogenic dyes. However, res color forming chromogenic dyes are sometimes used in admixture with the black color forming chromogenic dyes in order to effect tone adjustment of formed color from said black color forming chromogenic dyes used. On that account, it is desired that the red color forming chromogenic dyes as well as the black color forming chromogenic dyes are improved in chromogenic characteristics thereof.
Heretofore, 3-diethylamino-6-methyl-7-chlorofluoran of the formula, ##STR2## 3-diethylamino-7-chlorofluoran of the formula, ##STR3## or 3-diethylamino-7,8-benzofluoran of the formula, ##STR4## has preferably been used as a red color forming chromogenic dye for use in tone adjustment of the black color forming chromogenic dyes.